Pion production in two-body pd collisions

The reactions d(p, π⁺)t and d(p, π^o)³ He are analyzed in terms of the pp → π⁺d sub-process. The exclusion principle induces an additional exchange contribution involving the πd scattering amplitude. Acceptable deuteron and tritron (³H) wave functions which reproduce the charge form factors yield results consistent with experimental angular distributions at 470, 590, 754 and 1192 proton lab. energies. The forward peak is not sensitive to details of the wave functions. Both the direct and exchange form factors develop a zero which is imposed by the dip in the ³He charge form factor. The associated interference pattern governs the backward cross section.     

正负电子湮灭过程的核子激发态N*产生(英文)

目前,正负电子湮灭过程的核子激发态N*产生的实验数据主要来自于粲偶素能区。粲偶素衰变到核子激发态过程类似于其类时电磁形状因子测量过程,正反粲夸克短程湮灭提供了近乎于点源的胶子强子化过程。与γN,eN,πN反应互补,这一新的N*产生源具有同位旋和低自旋筛选的优势。综述了正负电子湮灭过程的核子激发态N*产生的实验情况和相关的唯象进展,同时讨论未来发展的一些新方向,如正负电子湮灭过程的核子激发态N*产物的一些新来源等。Up to now, the N* production from e+e- annihilations has been studied only around charmonium region. Charmonium decays to N*s are analogous to (time-like) EM form factors in that the charm quark annihilation provides a nearly pointlike (ggg) current. Complementary to other sources, such as πN, eN and γN reactions, this new source for N* spectroscopy has a few advantages, such as an isospin filter and a low spin filter. The experimental results on N* from e+e- annihilations and their phenomenological implications are reviewed. Possible new sources on N* production from e+e- annihilations are discussed.     

Backward elastic scattering and ϱ− production in π−p collisions at 10 GeV/c

The reactions π^?p → p π^? and π^?p → p?^? (?^? → π^?π⁰) at 10 GeV/c with the proton in the forward direction in the c.m.s. are discussed on the basis of 953 elastic scattering events and 2240 events of the reaction π^?p → pπ^?π⁰. The total backward cross sections are 0.52±0.10 and 1.52±0.28 μb, respectively. In both cases the production mechanism is compatible with the dominance of the baryonic Δ_δ Regge trajectory exchange. The ?^? decay angular distributions are studied in the u-channel helicity frame and the spin density matrix elements are presented as functions of u.     

Backward production of a spin-parity 1+ Kϱ resonance at 1.28 GeV

A (K_ππ)⁺ mass enhancement is observed in the reactions K^?p → Ξ ?K^o+π⁺π^o? when events with a small (K^? → Ξ^?) four momentum transfer squared are selected. The signal is also visible in the reaction K^?p → Ξ^?π⁺+ neutrals. The enhancement, centered at 1.28 GeV, is seen to decay preferentially into K? with spin-parity J^P = 1⁺. The cross section for K^?p→ Ξ^?C⁺(1.28) with C⁺ → K? at 4.15 GeV/c incident K^? momentum is (6.2 ± 0.6) μb.     

Resonance in the infra-red spectrum of N−

The free-free continuous absorption coefficient of N^- is calculated using multichannel theory and Hartree-Fock target functions. The ³P^e shape resonance due to e-N interactions gives rise to a resonance feature in the absorption coefficient.     

Origin of the N1 (1150) enhancement and the d1(2200) effect

Using pion exchange and Δ(1236) excitation inside the deuteron, the N¹(1150) enhancement with isospin $\text{I =}\text{1}\text{2}$, seen in evidence in dp coherent interactions, is explained. Good agreement is obtained, without any arbitrary normalization, between the Frascati-Caen-Saclay data and the predictions of this model. Its leading features and applications to other experiments are given.     

Limits on e±μ∓ production in pp collisions at the CERN ISR

A search for the reaction p+p → e^±μ^±+X at the CERN ISR gave no evidence for this process. Upper limits for e^±μ^?/e^+- are presented and are related to the branching fraction for leptonic decay of D(1.87).     

12C1 and 8Be production in 12C + 208Pb collisions

The mechanisms involved in the production of fast α-particles in ¹²C-induced reactions have been studied for the ¹²C + ²⁰⁸Pb system at the bombarding energies of E_12c = 132, 187 and 230 MeV. Absolute cross sections for the reactions ²⁰⁸Pb(¹²C. ¹²C¹→α + ⁸Be), ²⁰⁸Pb(¹²C, ⁸Be(g.s.)) and ²⁰⁸Pb(¹²C, ⁸Be(2.94 MeV)) have been determined by coincidence measurement of two or three correlated α-particles. Inclusive α-particle production cross sections were also measured at E_12c = 187 MeV. It is found that the inelastic process (¹²C, ¹²C¹→α + ⁸Be) does not contribute significantly to fast α-particle production but that the production of ⁸Be by projectile fragmentation is an important source of α-particles. At the highest bombarding energy (230 MeV) it appears that the ¹²C → 3α fragmentation reaction becomes more prominent at the expense of the ¹²C→α + ⁸Be fragmentation channel.     

K+ production in a cascade model for high-energy nucleus-nucleus collisions

The K⁺ production is studied for the p + NaF, Ne + NaF, Ne + Pb systems at 2.1 GeV/A in the frame of a 3-dimensional cascade model. Owing to the small elementary production cross sections, the K⁺ production is calculated perturbatively. Two kinds of production processes are introduced: baryon-baryon collisions leading to three-particle final states, and pion-nucleon collisions leading to two-body final states. The time evolution of the two processes is studied. The integrated K⁺ cross sections are in good agreement with the experimental data. The contribution of the πN induced mechanism is of the order of 25% for Ne + NaF, but increases with the size of the system. Scaling properties are discussed. A simple rescattering model is used to calculate the invariant cross section for the Ne + NaF case. Good agreement with experiment is obtained, except at forward angles.     

Jet production in e+e− collisions to order α3 and α4 and including QCD corrections

Cross sections for e⁺e^?→jet₁ + jet₂ + X are calculated to order α³ and α⁴ in the electromagnetic coupling and to arbitrary order in α_s in the leading logarithm approximation of QCD. Physically the processes included are the emission of hard protons from the incident e^± followed by annihilation, photon-proton scattering and deep inelastic scattering on an electron. The experimental separation of the mechanisms on the basis of their different event structure is discussed.     

Backward production of a spin parity 1+ϱπ enhancement at 1.04 GeV

A spin-parity 1⁺?π enhancement is observed for the 3π mass spectrum in the reaction K^?p → Σ^?π⁺π⁺π^? where events with a small (K^? → Σ^?) momentum transfer are selected. The mass (1040 MeV) and width (230 MeV) of this enhancement are reminiscent of the A₁ → ?π bump which has mainly been observed in the diffractive-like processes. The cross section for this enhancement at 4.15 GeV/c incident K^? momentum is (3.6 ± 0.5) μb.     

H- formation in H0++ Mg collisions

Absolute differential and total cross sections for H^- formation in H⁰ + Mg collisions have been measured over the energy range 1.0–5.0 keV. The differential cross section is strongly peaked in the forward direction and exhibits a shoulder at low energies. The total cross section has two pronounced maxima, and this structure is discussed.     

H− Formation in proton-metal collisions

Negative hydrogen ion formation is studied by scattering protons from a cesiated tungsten (110) surface. The primary energy ranges from 50 to 400 eV. The angle of incidence is 70° with respect to the surface normal. A maximum conversion efficiency $\text{H}{}^{\mathrm{?}}\text{(H}{}^{\mathrm{?}}\text{+ H}{}^0\text{)}$ of 67% is measured. The measurements can be described in terms of the probability model. The perturbation of the H^? ion by the metal is described within first order perturbation theory. A reasonable agreement between theory and experiment is obtained.     

N14 quadrupole coupling in some thermochromic and photochromic n-salicylideneanilines

In order to throw some light on the nature of the O-H--N hydrogen bond and on the mechanism responsible for thermochromism and photochromism in some solid N-salicylideneanilines, we determined by proton-nitrogen double resonance the N¹⁴ quadrupole coupling tensors of thermochromic salicylidene-3-chloroaniline, photochromic salicylidene-2-chloroaniline and of thermochromic 5′-chloro-salicylidene-aniline.     

Z0 boson associated b-jet production in high-energy nuclear collisions

The production of vector boson tagged heavy quark jets potentially provides new tools to probe the jet quenching effect. In this paper, we present the first theoretical study on the angular correlations (\begin{document}$ \Delta\phi_{bZ} $\end{document}), transverse momentum imbalance (\begin{document}$ x_{bZ} $\end{document}), and nuclear modification factor (\begin{document}$ I_{AA} $\end{document}) of \begin{document}$ Z^0 $\end{document} boson tagged b-jets in heavy-ion collisions, which was performed using a Monte Carlo transport model. We find that the medium modification of the \begin{document}$ \Delta\phi_{bZ} $\end{document} for \begin{document}$ Z^0$\end{document} + b-jet has a weaker dependence on \begin{document}$ \Delta\phi_{bZ} $\end{document} than that for \begin{document}$ Z^0$\end{document} + jet, and the modification patterns are sensitive to the initial jet \begin{document}$ p_T $\end{document} distribution. Additionally, with the high purity of the quark jet in \begin{document}$ Z^0$\end{document} + (b-) jet production, we calculate the momentum imbalance \begin{document}$ x_{bZ} $\end{document} and the nuclear modification factor \begin{document}$ I_{AA} $\end{document} of \begin{document}$ Z^0$\end{document} + b-jet in Pb+Pb collisions. We observe a smaller \begin{document}$ \Delta \langle x_{jZ} \rangle $\end{document} and larger \begin{document}$ I_{AA} $\end{document} of \begin{document}$ Z^0$\end{document} + b-jet in Pb+Pb collisions relative to those of \begin{document}$ Z^0$\end{document} + jet, which may be an indication of the mass effect of jet quenching and can be tested in future measurements.     

Measurement of D0, D+, Ds+ and D*+ production in fixed target 920?GeV proton–nucleus collisions

The inclusive production cross sections of the charmed mesons D⁰,D⁺,D_s ⁺ and D^*+ have been measured in interactions of 920 GeV protons on C, Ti, and W targets with the HERA-B detector at the HERA storage ring. Differential cross sections as a function of transverse momentum and Feynman’s x variable are given for the central rapidity region and for transverse momenta up to p_T=3.5 GeV/c. The atomic mass number dependence and the leading to non-leading particle production asymmetries are presented as well. PACS 13.85.Ni; 24.85.+p; 13.20.Fc     

Mutual recombination in slow Si^＋ ＋ H^- collisions

This paper studies the process of mutual neutralization of Si^＋ and H^- ions in slow collisions within the multichannel Landau-Zener model. All important ionic-covalent couplings in this collision system are included in the collision dynamics. The cross sections for population of specific final states of product Si atom are calculated in the CM energy range 0.05 e∨/u-5 ke∨/u. Both singlet and triplet states are considered. At collision energies below -10 e∨/u, the most populated singlet state is Si（3p4p, ^1S0）, while for energies above -150e∨/u it is the Si（3p, 4p, ^1P1） state. In the case of triplet states, the mixed 3p4p（^3S1 ＋^3P0） states are the most populated in the entire collision energy range investigated. The total cross section exhibits a broad maximum around 200 300e∨/u and for ECM ≤ 10e∨/u it monotonically increases with decreasing the collision energy, reaching a value of 8 × 10^-13 cm^2 at ECM = 0.05 e∨/u. The ion-pair formation process in Si（3p^2 ^3PJ）＋H（1s） collisions has also been considered and its cross section in the considered energy range is very small （smaller than 10^-20 cm^2 in the energy region below 1 ke∨/u）.     

An isobar model for the pd → tπ+ reaction

The differential cross section for the pd → tπ⁺ reaction is calculated at the three proton laboratory energies 400, 470 and 600 MeV. The triton wave function is taken to be of correlated Gaussian form, and the deuteron is one of the s-wave forms due to Hulthén, McGee and Paris. The pion production is considered to take place from intermediate states based on the five types of two-body correlations NΔ(⁵S₂, ⁵D₂, ⁵D₀) and NN(¹D₂, ¹S₀). The final cross sections are not in good agreement with experiment.     

A nucleon-nucleon potential that includes the effect of the N1(1236)

The transition potentials for the reaction $\text{N}\text{+}\text{N}\text{?}\text{N}\text{+}\text{N}{}^1\text{(1236)}$ and $\text{N}\text{+}\text{N}\text{?}\text{N}{}^1\text{(1236) +}\text{N}{}^1\text{(1236)+}\text{N}{}^1\text{(1236)}$ are derived in the case of the π and ? exchange using the quark model. The nucleon-nucleon scattering in the T=1, ¹S₀ state is treated as a coupled channel $\text{N}\text{+}\text{N}\text{?}\text{N}\text{+}\text{N}{}^1$ system.     

Backward production of ϱ0 and f0 mesons in π+n interactions at 6 GeV/c

Backward production of ?⁰ and f⁰ mesons in π⁺n interactions at 6 GeV/c is presented. Total and differential cross sections are reported along with spin density matrix elements.